‘Join’ FaceTime button inside iMessage

Hello, I was having trouble with a “Join” button appearing inside of my iMessage. Only one contact is affected; the other party is not experiencing a comparable problem. I have been trying to FaceTime that contact for days, but I am having problems.

It sounds like a setup error or malfunction. Check the FaceTime settings, make sure both of your iPhones are up to date, and try restarting them. For more help, get in touch with Apple Support if the problem continues.

Have you tried restarting your FaceTime app/phone?

I’ve experienced the same issue after calls ends. Though, it resolves itself within a few minutes.